As the density of semiconductor devices increases, however, the resistance capacitance (RC) delay time increasingly dominates the circuit performance. To reduce the RC delay, there is a desire to switch from conventional dielectrics to low-k dielectrics, which have a dielectric constant less than SiO2 or about 4 to prevent cross-talk between the different levels of metalization and to reduce device power consumption. Low-k dielectrics may also include a class of low-k dielectrics frequently called extreme low-k (ELK) dielectrics, which have a dielectric constant less than about 2.5. One of current ELK materials is a porous low-k material, which is particularly useful as inter-metal dielectrics (IMDs) and as interlayer dielectrics (ILDs) for sub-micron technology, or even for 65 nm node or 45 nm node or beyond technology. The porous low-k dielectric materials produced by spin-on and chemical vapor deposition processes or by a self-assembly process typically require a curing process subsequent to the deposition. Instead of thermally curing or plasma treating, the porous low-k dielectrics can be UV cured at substantially shorter times or at lower temperatures to eliminate the need for prior furnace curing and therefore reducing the total thermal budget, while maintaining or reducing the dielectric constant. However, during the UV curing process, the porous low-k dielectric layer (i.e., a porogen doped SiCO film) only absorbs about 40% UV light, while 60% UV light passes through underlying layers. This causes a decrease in UV curing efficiency that needs longer cure time and lower WPH. The UV penetration issue also degrades the film adhesion of the under layers (i.e., the adhesion between an etch-stop layer and a copper interconnect) that may requires an additional curing process on the cured ELK dielectric layer and front-end of the line (FEOL) devices.
There is therefore a need in the integrated circuit manufacturing art to develop a manufacturing process whereby porous low-k dielectric layers may be formed to improve UV curing efficiency and eliminate the UV penetration issue.